Plasma processor

BACKGROUND OF THE INVENTION

0001The present invention relates to a plasma processing apparatus which performs a predetermined process by generating a plasma.

0002In the manufacture of a semiconductor device or flat panel display, plasma processing apparatuses are used often to perform processes such as formation of an oxide film, crystal growth of a semiconductor layer, etching, and ashing. A case wherein a plasma processing apparatus is applied to an etching apparatus will be described. <figref idref="DRAWINGS">FIG. 9</figref> is a view showing an arrangement of an etching apparatus using a conventional plasma processing apparatus.

0003A susceptor <b>521</b> having a support surface for placing a wafer W thereon and an upper electrode <b>531</b> parallel to the support surface of the susceptor <b>521</b> are arranged in a process chamber <b>511</b>. The susceptor <b>521</b> also serves as a lower electrode.

0004Exhaust ports <b>513</b> for evacuating the interior of the process chamber <b>511</b> to a predetermined vacuum degree are formed in the bottom of the process chamber <b>511</b>, and a gas supply nozzle <b>514</b> for supplying process gases into the process chamber <b>511</b> is provided to the side wall of the process chamber <b>511</b>.

0005The upper electrode <b>531</b> is connected to an RF power supply <b>534</b>, which outputs an RF power of, e.g., 60 MHz, through a matching circuit <b>535</b>. When the power supply <b>534</b> starts supplying the RF power with a frequency of 60 MHz to the upper electrode <b>531</b>, an electric field with a frequency of 60 MHz is formed in the space between the upper electrode <b>531</b> and susceptor <b>521</b>. This electric field ionizes the gases supplied from the gas supply nozzle <b>514</b> to generate a plasma P. The plasma P is utilized for etching the wafer W placed on the support surface of the susceptor <b>521</b>.

0006When performing an etching process, the distribution of the plasma P is preferably not distributed in the entire process chamber <b>511</b> but distributed over the support surface of the susceptor <b>521</b> with a high density. This is because with this distribution, the etching process can be performed efficiently and etching of the inner wall surface of the process chamber <b>511</b> by the plasma P can be suppressed, so that the service life of the process chamber <b>511</b> can be prolonged.

0007In view of this, according to this etching apparatus, a filter <b>527</b> formed of an LC series resonance circuit is inserted between the susceptor <b>521</b> and ground. The resonance frequency of the filter <b>527</b> is set to 60 MHz, which is the same as the frequency of the RF power to be supplied to the upper electrode <b>531</b>. For example, if L=0.07 μH and C=100 pF, the resonance frequency of the filter <b>527</b> can be set to 60 MHz. The frequency characteristics of the filter <b>527</b> are as indicated by a solid line in <figref idref="DRAWINGS">FIG. 10</figref>, and the impedance is the minimum when the frequency is 60 MHz.

0008When the plasma P is generated, however, an ion sheath SH is formed between the plasma bulk and the upper electrode <b>531</b> or susceptor <b>521</b>. An electric field is formed in the layer of the ion sheath SH, and accordingly a new capacitance is generated between the upper electrode <b>531</b> and susceptor <b>521</b> by the generation of the plasma P. For example, assume that a capacitance of 200 pF is generated by the ion sheath SH. Even when the resonance frequency of the filter <b>527</b> is designed at 60 MHz as described above, the frequency characteristics of the first path extending from the upper electrode <b>531</b> to reach ground through the susceptor <b>521</b> and filter <b>527</b> are as indicated by a broken line in <figref idref="DRAWINGS">FIG. 10</figref>, and the resonance frequency of the first path becomes 74 MHz. Hence, even if the filter <b>527</b> is designed without considering the influence of the ion sheath SH as in the prior art, the frequency of the RF power cannot cause resonance when the plasma P is generated, so the impedance of the first path cannot be decreased sufficiently. Consequently, the plasma P cannot be sufficiently concentrated on the support surface of the susceptor <b>521</b>.

0009When process conditions such as the power value of the RF power to be supplied to the upper electrode <b>531</b>, the pressure in the process chamber <b>511</b>, the type and mixing ratio of the process gases, and the like are changed, the capacitance obtained by the ion sheath SH described above also changes. Accordingly, even when the filter <b>527</b> is designed with a consideration to the influence of the ion sheath SH formed when a plasma is generated under predetermined process conditions, if the process conditions differ from the predetermined process conditions, the frequency (e.g., 60 MHz) of the RF power cannot cause resonance.

0010When the etching process is to be performed, the plasma P is preferably concentratedly distributed on the support surface of the susceptor <b>521</b>, as described above. When the interior of the process chamber <b>511</b> is to be cleaned, the plasma P is rather preferably diffused in the entire process chamber <b>511</b>. In this manner, preferable plasma distribution differs depending on the object of the process. Conventionally, the filter <b>527</b> is designed for the etching process, and accordingly its characteristics are fixed. Hence, the interior of the process chamber <b>511</b> cannot be cleaned under preferable conditions.

0011When deposits attaching to the inner wall surface or the like of the process chamber <b>511</b> peel off during the etching process and form particles, the particles attach to the wafer W to decrease the yield of elements to be formed on the wafer W. Therefore, desirably no deposit preferably attaches at all to the inner wall surface of the like of the process chamber <b>511</b>, or if any, they desirably attach stably so they will not peel off during the process. The deposit attaching state, however, changes depending on the process conditions as described above. When the process is performed after changing the process condition, the deposit attaching state changes to form particles, which may decrease the yield.

0012The above problems arise not only when the plasma processing apparatus is applied to an etching apparatus, but are common among plasma processing apparatuses.

SUMMARY OF THE INVENTION

0013The present invention has been made to solve the above problems, and has as its object to realize a preferable plasma distribution in accordance with the object of the plasma process.

0014In order to achieve the above object, the present invention is characterized by comprising a first filter connected between ground and a susceptor which is arranged in a process chamber to place a target object thereon, and having variable circuit characteristics, a sensor which detects a state of a plasma generated in the process chamber, and control means for controlling the circuit characteristics of the first filter on the basis of a detection result output from the sensor. Thus, the impedance of the first path, which extends from electric field generating means for generating an AC electric field at a position opposing the support surface of the susceptor to ground through the susceptor and filter, can be adjusted in accordance with the state of the plasma.

0015In order to perform a process such as etching or CVD, if the plasma distributed over a region opposing the support surface of the susceptor is to be maximized, the control means may control the circuit characteristics of the first filter in such a direction that the impedance of the first path decreases (this mode is called the first control mode). In order to clean the interior of the process chamber, if the plasma is to be diffused in the entire process chamber so the plasma reaching the inner wall surface of the process chamber is maximized, the control means may control the circuit characteristics of the first filter in such a direction that the impedance of the first path increases (this mode is called the second control mode).

0016When the state of the plasma is detected in this manner and the circuit characteristics of the first filter are controlled on the basis of the detection result, even if a plasma is generated to form an ion sheath or even if the state of the ion sheath changes, a plasma distribution appropriate for a plasma process can be realized without being adversely affected by the ion sheath or its change.

0017In the case of a parallel-plate plasma processing apparatus, the electric field generating means comprises a counter electrode arranged to be parallel to the support surface of a susceptor, and a power supply for supplying an RF power to the electrode. The sensor suffices as far as it detects, e.g., the value of a current flowing through the first filter, the value of a voltage applied to the first filter, the phase difference between the current and voltage, the value of a current flowing through the counter electrode, the value of the voltage applied to the counter electrode, the phase difference between the current/voltage of the first filter and the current/voltage of the counter electrode, or the like. An output signal from a sensor attached to the wall (excluding the susceptor and counter electrode) or window of the process chamber may be used to control the first filter. Alternatively, output signals from sensors may be used together.

0018The control means may have a switch that performs switching operation between the first control mode and the second control mode in a multilevel manner or arbitrarily. The two control modes can be realized by the switching operation. Thus, not only a process such as etching but also cleaning can be performed in a preferable state.

0019The control means may perform switching operation among a plurality of control modes, thus realizing a predetermined plasma distribution corresponding to each of the control modes in the process chamber. Hence, even if the process conditions change and the state of a deposit attaching to the inner wall surface of the process chamber changes, if the amount of plasma reaching the inner wall surface of the process chamber is adjusted in accordance with the changed state, deposits can be suppressed from peeling off to form particles.

0020The control means may have the function of changing the circuit characteristics of the first filter during a process. For example, the amount of plasma reaching the inner wall surface of the process chamber may be changed periodically, or the amount of plasma reaching the inner wall surface may be changed on the basis of the temperature or the like of the wall of the process chamber. Then, the deposit attaching to the inner wall surface of the process chamber can be stabilized.

0021When the sensor is of a type that detects the value of a current flowing through the first filter, the control means may control the circuit characteristics of the first filter in such a direction that the value of the current increases if the first control mode is selected, and may control the circuit characteristics of the first filter in such a direction that the value of the current decreases if the second control mode is selected.

0022When the sensor is of a type that detects the value of a voltage applied to the first filter, the control means may control the circuit characteristics of the first filter in such a direction that the value of the voltage decreases if the first control mode is selected, and may control the circuit characteristics of the first filter in such a direction that the value of the voltage increases if the second control mode is selected.

0023When the sensor is of a type that detects the number of ions reaching a predetermined region of the inner wall surface of the process chamber, the control means may control the circuit characteristics of the first filter in such a direction that the number of ions decreases if the first control mode is selected, and may control the circuit characteristics of the first filter in such a direction that the number of ions increases if the second control mode is selected.

0024The control means may control the circuit characteristics of the first filter to match a value obtained by arithmetic process of the detection result output from a single or a plurality of sensors. Then, more appropriate control can be performed than in a case wherein the detection result is directly used for control.

0025The present invention further may further comprise a power supply connected to the susceptor to apply a bias across the susceptor and the electric field generating means, and a second filter connected between the electric field generating means and ground and having variable circuit characteristics. The control means may control the circuit characteristics of the second filter on the basis of in the detection result output from the sensor. When a bias is applied across the susceptor and electric field generating means, the energy and anisotropy of the plasma can be controlled. At this time, the impedance of the second path extending from the susceptor to ground through the electric field generating means and the second filter can be adjusted in accordance with the state of the plasma. Even if a plasma is generated to form an ion sheath or even if the state of the ion sheath changes, correct control can be performed without being adversely affected by the ion sheath or its change.

0026The sensor suffices as far as it detects, e.g., the value of a current flowing through the second filter, the value of a voltage applied to the second filter, the phase difference between the current and voltage, the value of a current flowing through the susceptor, the value of the voltage applied to the susceptor, the phase difference between the current/value of the second filter and the current/voltage of the susceptor, or the like. An output signal from a sensor attached to the wall (excluding the susceptor and counter electrode) or window of the process chamber may be used to control the second filter. Alternatively, output signals from sensors may be used together.

0027When the sensor is of a type that detects the value of a current flowing through the second filter, the control means may control the circuit characteristics of the second filter in such a direction that the value of the current increases.

0028When the sensor is of a type that detects the value of a voltage applied to the second filter, the control means may control the circuit characteristics of the second filter in such a direction that the value of the voltage decreases.

0029When the sensor is of a type that detects the number of ions reaching a predetermined region of the inner wall surface of the process chamber, the control means may control the circuit characteristics of the second filter in such a direction that the number of ions decreases.

0030The control means may control the circuit characteristics of the first and second filters to match a value obtained by arithmetic process of the detection result output from a single or a plurality of sensors. Then, more appropriate control operation can be performed than a case wherein the detection result is directly used for control.

0031The control means may appropriately control the circuit characteristics of the first filter such that occurrence of abnormal discharge in the process chamber is suppressed. Alternatively, the control means may appropriately control the circuit characteristics of the first and second filters such that occurrence of abnormal discharge in the process chamber is suppressed.

0032The first filter may be formed to include an inductance of not less than 5 μH or a capacitance of not more than 1,000 pF or. Alternatively, the first and second filters may be formed to include an inductance of not less than 5 μH or a capacitance of not more than 1,000 pF. Then, even when the inductance and capacitance obtained by the ion sheath change in accordance with the process conditions, the impedances of the first and second paths can be adjusted easily in accordance with the state of the plasma by only slightly changing the circuit characteristics of the filters, or even without changing them at all.

0033The first filter may have a first module for blocking a DC component from passing therethrough, and a second module with a variable circuit constant against a frequency of an AC electric field. When a bias power supply is connected to the susceptor, the first filter may also have a third module for blocking a frequency component of the bias from passing therethrough. In this case, the first filter may have a blocking plate for electrostatically or electromagnetically blocking the first and second modules and the third module from each other.

0034The second filter may have a first module for blocking a DC component from passing therethrough, a second module with a variable circuit constant against the frequency of the bias, and a third module for blocking the frequency component of the RF electric field from passing therethrough. In this case, the second filter may have a blocking plate for electrostatically or electromagnetically blocking the first and second modules and the third module from each other.

BRIEF DESCRIPTION OF DRAWINGS

0035<figref idref="DRAWINGS">FIG. 1</figref> is a view showing the arrangement of an etching apparatus according to the first embodiment of the present invention;

0036<figref idref="DRAWINGS">FIG. 2</figref> is a circuit diagram showing the arrangement of a first filter;

0037<figref idref="DRAWINGS">FIG. 3</figref> is a view showing the arrangement of the sensor shown in <figref idref="DRAWINGS">FIG. 1</figref>;

0038<figref idref="DRAWINGS">FIG. 4</figref> is a graph showing the frequency characteristics of a first path extending from an upper electrode to reach ground through a susceptor and filter;

0039<figref idref="DRAWINGS">FIG. 5</figref> is a view showing the arrangement of an etching apparatus according to the second embodiment of the present invention;

0040<figref idref="DRAWINGS">FIG. 6</figref> is a view showing the arrangement of an etching apparatus according to the third embodiment of the present invention;

0041<figref idref="DRAWINGS">FIG. 7</figref> is a circuit diagram showing the arrangement of a second filter;

0042<figref idref="DRAWINGS">FIG. 8</figref> is a view showing an arrangement in which the first filter and a matching circuit are integrally formed;

0043<figref idref="DRAWINGS">FIG. 9</figref> is a view showing an arrangement of an etching apparatus using a conventional plasma processing apparatus; and

0044<figref idref="DRAWINGS">FIG. 10</figref> is a graph showing the frequency characteristics of the filter used in the etching apparatus shown in <figref idref="DRAWINGS">FIG. 9</figref>, and the frequency characteristics of a path extending from the upper electrode to reach ground through a susceptor and filter.

DETAILED DESCRIPTION OF THE EMBODIMENTS

0045The embodiments of the present invention will be described in detail with reference to the drawings. A case will be described wherein the present invention is applied to an etching apparatus.

First Embodiment

0046<figref idref="DRAWINGS">FIG. 1</figref> is a view showing the arrangement of an etching apparatus according to the first embodiment of the present invention. In <figref idref="DRAWINGS">FIG. 1</figref>, part of the arrangement shows its sectional structure.

0047A process chamber <b>11</b> of this etching apparatus is defined in a hermetically closeable cylindrical process vessel <b>12</b>. The process vessel <b>12</b> is made of a conductive material such as aluminum. Exhaust ports <b>13</b> communicating with a vacuum pump (not shown) are formed in the bottom of the process vessel <b>12</b>, and can set the process chamber <b>11</b> to a predetermined vacuum degree.

0048A support table <b>22</b> is provided to the bottom of the process vessel <b>12</b> through an insulating plate <b>23</b>, and a cylindrical columnar susceptor <b>21</b> is fixed on the support table <b>22</b>. The susceptor <b>21</b> has a horizontal support surface for placing a wafer (target object) W as an etching target thereon. The susceptor <b>21</b> also serves as a lower electrode, and is made of a conductive material such as aluminum.

0049A circular disk-like upper electrode <b>31</b> having a plurality of through holes <b>31</b>A is arranged in the upper space of the process chamber <b>11</b> to be parallel to the support surface of the susceptor <b>21</b>. The upper electrode <b>31</b> is made of a conductive material such as single-crystal silicon, and is fixed to the lower portion of a support <b>32</b>.

0050The support <b>32</b> is made of a conductive material such as aluminum, and forms a hollow circular column in it to have the upper electrode <b>31</b> as its bottom surface. The support <b>32</b> is so attached as to close the upper opening of the process vessel <b>12</b> through an insulating ring <b>33</b>. A gas inlet port <b>32</b>A is formed at the center of the upper surface of the support <b>32</b>, and is connected to a gas inlet pipe <b>39</b>. Process gases such as Ar, O₂, and the like are introduced from the gas inlet pipe <b>39</b>.

0051An RF power supply <b>34</b> is connected to the support <b>32</b> having the same potential as that of the upper electrode <b>31</b>. The RF power supply <b>34</b> suffices as far as it outputs an RF power with a frequency of about several ten MHz and a power value of about 5 kW. In this embodiment, note that the RF power supply <b>34</b> outputs an RF power with a frequency of 60 MHz and a power value of 3.3 kW. A matching circuit <b>35</b> is connected between the RF power supply <b>34</b> and support <b>32</b> to match their impedances. For example, the matching circuit <b>35</b> is formed of a variable capacitor, and its capacitance is controlled by a controller <b>36</b>.

0052The susceptor <b>21</b> is grounded through a first filter <b>27</b> formed of a resonance circuit having a variable reactance. The path extending from the upper electrode <b>31</b> to reach ground through the susceptor <b>21</b> and filter <b>27</b> will be called the first path. When the reactance of the filter <b>27</b> is changed, the impedance of the first path against the frequency (60 MHz) of the RF power supplied to the upper electrode <b>31</b> can be adjusted.

0053Furthermore, a sensor <b>28</b> for detecting an electrical signal flowing through the filter <b>27</b> on the basis of the state of a plasma P generated in the process chamber <b>11</b>, and a controller for controlling the reactance of the filter <b>27</b> on the basis of a detection result output from the sensor <b>28</b> are provided. In the etching apparatus shown in <figref idref="DRAWINGS">FIG. 1</figref>, the controller <b>36</b> for the matching circuit <b>35</b> is provided with the function of the control means for the filter <b>27</b>. Alternatively, a control means for the filter <b>27</b> may be provided separately.

0054The filter <b>27</b> will be further described.

0055<figref idref="DRAWINGS">FIG. 2</figref> is a circuit diagram showing the arrangement of the filter <b>27</b>. The filter <b>27</b> has a first module <b>27</b>A for blocking a DC component from passing therethrough, and a second module <b>27</b>B with a variable reactance against the frequency of the RF power supplied to the upper electrode <b>31</b>.

0056When the RF power supply <b>34</b> supplies the RF power to the upper electrode <b>31</b>, a DC voltage of about several hundred V is generated in the susceptor <b>21</b>. The first module <b>27</b>A is formed of, e.g., a capacitor <b>27</b><i>p</i>, and blocks a DC component from passing from the susceptor <b>21</b> to ground, so that short-circuiting of the DC component can be prevented.

0057The second module <b>27</b>B is formed of, e.g., a series circuit (LC series resonance circuit) of a coil <b>27</b><i>r </i>and capacitor <b>27</b><i>q</i>. In this case, it suffices as far as at least one of the inductance of the coil <b>27</b><i>r </i>and the capacitance of capacitor <b>27</b><i>q </i>is variable. In this embodiment, note that the inductance of the coil <b>27</b><i>r </i>is variable, while the capacitance of the capacitor <b>27</b><i>q </i>is fixed. When the second module <b>27</b>B is an LC series resonance circuit as shown in <figref idref="DRAWINGS">FIG. 2</figref>, the capacitor <b>27</b><i>q </i>of the second module <b>27</b>B can also serve as the capacitor <b>27</b><i>p </i>of the first module <b>27</b>A.

0058The reactance of the filter <b>27</b> which is formed of an inductance L (that is, the inductance of the coil <b>27</b><i>r</i>) and capacitance C (that is, synthetic capacitance of the capacitors <b>27</b><i>p </i>and <b>27</b><i>q</i>) is designed by considering an inductance L_SHand capacitance C_SHobtained by an ion sheath SH and the structures of the process vessel <b>12</b> and electrodes (susceptor <b>21</b> and upper electrode <b>31</b>), such that under predetermined process conditions a resonance frequency f1 of the first path is equal to the frequency (60 MHz) of the RF power supplied to the upper electrode <b>31</b> and the impedance for this frequency is the minimum. Note that the range of the reactance of the filter <b>27</b> is set such that the impedance of the first path can be minimized even when the inductance L_SHand capacitance C_SHobtained by the ion sheath SH change in accordance with the process conditions, and such that the impedance of the first path can be sufficiently increased when the interior of the process chamber <b>11</b> is to be cleaned.

0059For example, the filter <b>27</b> is designed under the following process conditions: <ul id="ul0001" list-style="none"><li id="ul0001-0001" num="0000"><ul id="ul0002" list-style="none"><li id="ul0002-0001" num="0060">frequency of RF power: 60 MHz, power value: 1.0 kW to 5.0 kW</li><li id="ul0002-0002" num="0061">process pressure: 0.6 Pa to 10 Pa</li><li id="ul0002-0003" num="0062">process gases: Ar=100 sccm to 500 sccm, <ul id="ul0003" list-style="none"><li id="ul0003-0001" num="0063">O₂=5 sccm to 15 sccm</li></ul></li></ul></li></ul>

0064(sccm=standard cubic centimeter per minute)

0065The capacitance C_SHobtained by the ion sheath SH which is formed when the plasma P is generated under these conditions is about 100 pF to 300 pF. The resonance frequency f1 of the first path including the filter <b>27</b> is expressed as follows: <br /><i>f</i>1=1/{2π(<i>LC</i>₁)^1/2}  (1)<br /><i>C</i>1=<i>C·C</i>_SH/(<i>C+C</i>_SH))  (2)<br /> Note that C=200 pF and 50 nH≦L≦100 nH are set so that f1=60 MHz is obtained for C_SH=200 pF.

0066Alternatively, the filter <b>27</b> may be formed by using a fixed inductance L sufficiently larger than the upper limit of the variable range of the inductance LSH obtained by the ion sheath SH or sufficiently smaller than the lower limit of the variable range of the capacitance C_SHobtained by the ion sheath SH. In this case, the fixed inductance L is set to 5 μH or more and the fixed capacitance C is set to 1,000 pF or less. Then, the range of the reactance of the filter <b>27</b> can be set such that even if the inductance L_SHand capacitance C_SHof the ion sheath SH change in accordance with the process conditions, the impedance of the first path can be minimized or increased to be sufficiently large without being adversely affected by the changes in inductance L_SHand capacitance C_SH.

0067Alternatively, the filter <b>27</b> may be formed of only the capacitor <b>27</b><i>q</i>, and the LC resonance circuit may be formed by utilizing the inductance of an interconnection that connects the susceptor <b>21</b> to ground through the filter <b>27</b>.

0068The sensor <b>28</b> will be further described.

0069<figref idref="DRAWINGS">FIG. 3</figref> is a view showing the arrangement of the sensor <b>28</b>. The sensor <b>28</b> is formed of an RF current sensor <b>28</b>A which detects the value of the current flowing through the filter <b>27</b> and outputs it to the controller <b>36</b>, and an RF voltage sensor <b>28</b>B which detects the value of the voltage applied to the filter <b>27</b> and outputs it to the controller <b>36</b>.

0070When filters (not shown) which pass only 60 MHz are inserted on the output sides of the current sensor <b>28</b>A and voltage sensor <b>28</b>B, respectively, only the frequency of the RF power supplied to the upper electrode <b>31</b> can be detected accurately.

0071The controller <b>36</b> serving as the control means for the filter <b>27</b> will be further described.

0072When the sensor <b>28</b> comprises the current sensor <b>28</b>A and voltage sensor <b>28</b>B, the controller <b>36</b> has the function of obtaining a phase difference between the current and voltage detected by the sensor <b>28</b> and calculating the power consumption value of the filter <b>27</b>, and the function of controlling the reactance of the filter <b>27</b> on the basis of the detected current value or voltage value and the calculated power value. Alternatively, an RF equivalent circuit of the process vessel <b>12</b> may be stored in the controller <b>36</b> in advance, so the controller <b>36</b> has the function of calculating a current flowing through the susceptor <b>21</b> and the side wall of the process vessel <b>12</b> from the output of the filter <b>27</b>, thus controlling the reactance of the filter <b>27</b>.

0073Regarding reactance control of the filter <b>27</b>, it may be performed alone, or may be performed in combination with capacitance control of the matching circuit <b>35</b> in accordance with a predetermined sequence.

0074The controller <b>36</b> has a switch (not shown) that performs switching operation between the first control mode of controlling such that the plasma P distributed over a region opposing the support surface of the susceptor <b>21</b> becomes maximum, and the second control mode of controlling such that the plasma P reaching the inner wall surface of the process chamber <b>11</b> becomes maximum. The first control mode is selected when performing an etching process. The second control mode is selected when performing cleaning.

0075When the first control mode is selected, the controller <b>36</b> controls the reactance of the filter <b>27</b> such that the impedance of the first path against the frequency of the RF power supplied to the upper electrode <b>31</b> becomes minimum. For example, the capacitance C of the e filter <b>27</b> is controlled such that the value of the current flowing through the filter <b>27</b> becomes maximum. When the second control mode is selected, the controller <b>36</b> controls the reactance of the filter <b>27</b> such that the impedance of the first path against the frequency of the RF power becomes sufficiently large. For example, the capacitance C of the filter <b>27</b> is controlled such that the value of the current flowing through the filter <b>27</b> becomes sufficiently small.

0076In this manner, the controller <b>36</b> may perform control on the basis of the value itself of the current flowing through the filter <b>27</b>. More preferably, the controller <b>36</b> estimates and controls the total current input to the susceptor <b>21</b> by considering the current flowing from the susceptor <b>21</b> to other members and circuits such as an insulator (not shown).

0077The reactance of the filter <b>27</b> may be controlled such that the value of the voltage applied to the filter <b>27</b> becomes large or small.

0078As described above, the detection result output from the sensor <b>28</b> as the detected current value or voltage value may be directly used for control. Alternatively, a value obtained by applying the detection result to a predetermined model and subjecting it to an arithmetic process may be used for control. The model means an expression for calculating an index indicating the plasma distribution in the process chamber <b>11</b> at a given time from, e.g., the value of the current passing through the filter <b>27</b>. When this model is used, more appropriate control can be performed.

0079The operation of the etching apparatus shown in <figref idref="DRAWINGS">FIG. 1</figref> will be described.

0080The operation during the etching process will be described first.

0081First, with the wafer W being placed on the support surface of the susceptor <b>21</b>, the interior of the process chamber <b>11</b> is set to a vacuum degree of, e.g., about 2.7 Pa. While maintaining this vacuum degree, Ar and O₂are introduced from the gas inlet pipe <b>39</b> to the space between the support <b>32</b> and upper electrode <b>31</b> at flow rates of 400 sccm. These gases diffuse in the space and are supplied into the process chamber <b>11</b> through the plurality of through holes <b>31</b>A formed in the upper electrode <b>31</b>. The gases supplied into the process chamber <b>11</b> at this time are uniformly discharged to the target surface of the wafer W.

0082In this state, the RF power supply <b>34</b> supplies an RF power with a frequency of 60 MHz and a power value of 3.3 kW to the upper electrode <b>31</b>. The RF power forms an AC field with a frequency of 60 MHz in the process chamber <b>11</b>, and flows to ground from the susceptor <b>21</b> or process vessel <b>12</b>. The electric field formed in the process chamber <b>11</b> ionizes the gases supplied in the process chamber <b>11</b> to generate the plasma P. At this time, the ion sheath SH accompanying an electric field is formed around the plasma P. The ion sheath SH newly generates a capacitance C_SHof about 200 pF between the upper electrode <b>31</b> and susceptor <b>21</b>.

0083When the plasma P stabilizes, the filter <b>27</b> detects the value of the current flowing through the filter <b>27</b> interposed between the susceptor <b>21</b> and ground and the value of the voltage across the filter <b>27</b>, and outputs them to the controller <b>36</b>. The controller <b>36</b> calculates the value of the power from the detected current value and voltage value. In the controller <b>36</b>, the first control mode appropriate for the etching process has been selected. Thus, the controller <b>36</b> controls the reactance of the filter <b>27</b> in such a direction that the detected current value increases, and decreases the impedance of the first path extending from the upper electrode <b>31</b> to ground through the susceptor <b>21</b> and filter <b>27</b>.

0084<figref idref="DRAWINGS">FIG. 4</figref> is a graph showing the frequency characteristics of the first path including the filter <b>27</b>. The solid line indicates the characteristics of the resonance frequency f1 being 60 MHz, and the broken line indicates the characteristics of the resonance frequency f1 being 74 MHz. As is apparent from <figref idref="DRAWINGS">FIG. 4</figref>, the impedance of the first path against 60 MHz becomes minimum when the resonance frequency f1 of the first path is 60 MHz. Accordingly, the capacitance C of the filter <b>27</b> is controlled such that the resonance frequency of the first path becomes 60 MHz. When the capacitance C of the filter <b>27</b> is 200 pF and a capacitance C_SHof about 100 pF to 300 pF is generated due to the influence of the ion sheath SH, the inductance L of the filter <b>27</b> is adjusted within a range of almost 50 nH to 110 nH, as is apparent from equations (1) and (2).

0085Detection with the sensor <b>28</b> and control of the filter <b>27</b> with the controller <b>36</b> on the basis of this detection result may be performed once, and after that the two detection results may be fixed. Alternatively, detection and control may be repeated when necessary.

0086In this manner, control operation is performed on the basis of the current flowing through the filter <b>27</b> such that the impedance of the first path against 60 MHz becomes minimum. Then, of the RF power supplied to the upper electrode <b>31</b>, its proportion directed to the process vessel <b>12</b> decreases as compared to the prior art, and its proportion directed to the susceptor <b>21</b> further increases. Hence, the distribution of the plasma P generated by the RF power does not spread in the entire process chamber <b>11</b> but is concentrated to the support surface of the susceptor <b>21</b>. As a result, the etching process of the wafer W utilizing the plasma P can be performed more efficiently than in the prior art. The amount of plasma P reaching the inner wall surface of the process vessel <b>12</b> decreases as compared to the prior art. Thus, etching of the inner wall surface of the process vessel <b>12</b> by the plasma P is suppressed, so that the service life of the process vessel <b>12</b> can be prolonged and formation of the particles can be decreased.

0087A case wherein etching process is to be performed under different process conditions will be described. For example, the process conditions are changed as follows: <ul id="ul0004" list-style="none"><li id="ul0004-0001" num="0000"><ul id="ul0005" list-style="none"><li id="ul0005-0001" num="0088">frequency of RF power: 60 MHz, power value: 1.0 kW to 1.5 kW</li><li id="ul0005-0002" num="0089">process pressure: 2.7 Pa</li><li id="ul0005-0003" num="0090">process gases: Ar=300 sccm to 400 sccm, <ul id="ul0006" list-style="none"><li id="ul0006-0001" num="0091">O₂=5 sccm to 20 sccm</li></ul></li></ul></li></ul>

0092Under these conditions, a capacitance C_SHof about 300 pF to 400 pF is generated by the ion sheath SH. When the inductance L of the filter <b>27</b> is adjusted within the range of about 50 nH to 60 nH by the same control as that described above, the resonance frequency of the first path is set to 60 MHz, so that the impedance of the first path against 60 MHz can be minimized. Even when the process conditions are changed and accordingly the state of the ion sheath SH changes, a plasma distribution appropriate for the etching process can be realized without preparing a filter designed to match the process conditions.

0093Cleaning of the interior of the process chamber <b>11</b> will be described. Operations until generation of the plasma P and calculation of the power consumption value of the filter <b>27</b> are the same as in the etching process.

0094When cleaning is to be performed, as the second control mode is selected in the controller <b>36</b>, the controller <b>36</b> controls the reactance of the filter <b>27</b> in such a direction that the value of the detected current decreases, thus increasing the impedance of the first path extending from the upper electrode <b>31</b> to reach ground through the susceptor <b>21</b> and filter <b>27</b>.

0095As is apparent from <figref idref="DRAWINGS">FIG. 4</figref>, the impedance of the first path against 60 MHz increases as the resonance frequency f1 of the first path changes from 60 MHz. Accordingly, in this case, the inductance L of the filter <b>27</b> is controlled such that the resonance frequency of the first path largely changes from 60 MHz (excitation frequency). The resonance of the first path may alternatively be set at a higher or lower frequency.

0096In this manner, control is performed on the basis of the current flowing through the filter <b>27</b> such that the impedance of the first path against 60 MHz increases. Then, of the RF power supplied to the upper electrode <b>31</b>, its proportion directed to the susceptor <b>21</b> decreases, and its proportion directed to the process vessel <b>12</b> increases. Hence, the distribution of the plasma P generated by the RF power spreads in the entire process chamber <b>11</b>, and the plasma P reaching the inner wall surface of the process chamber <b>11</b> increases. Thus, the interior of the process chamber <b>11</b> can be cleaned efficiently.

0097In this manner, the controller <b>36</b> can be switched between the two control modes by the switch. Thus, not only the etching process but also cleaning can be performed in a preferable state.

0098In the etching apparatus shown in <figref idref="DRAWINGS">FIG. 1</figref>, the voltage sensor <b>28</b>B may detect the value of the voltage applied to only the capacitors <b>27</b><i>p </i>and <b>27</b><i>q </i>or the coil <b>27</b><i>r </i>that form part of the filter <b>27</b>.

0099The sensor <b>28</b> may be formed of only the current sensor <b>28</b>A. In this case, the controller <b>36</b> controls the reactance of the filter <b>27</b> in such a direction that the value of the current flowing through the filter <b>27</b> increases or decreases. In this case as well, the controller <b>36</b> preferably estimates and controls the total current input to the susceptor <b>21</b>.

0100Although the reactance of the filter <b>27</b> is variable, it suffices as far as the circuit characteristics of the filter <b>27</b> including a resistance are variable.

0101To minimize the impedance of the first path, a resonance frequency need not be used. It suffices as far as the impedance is minimized as a consequence.

Second Embodiment

0102<figref idref="DRAWINGS">FIG. 5</figref> is a view showing the arrangement of an etching apparatus according to the second embodiment of the present invention. In <figref idref="DRAWINGS">FIG. 5</figref>, the same portions as in <figref idref="DRAWINGS">FIG. 1</figref> are denoted by the same reference numerals, and a description thereof will be omitted when appropriate.

0103The etching apparatus shown in <figref idref="DRAWINGS">FIG. 5</figref> has a quadrupole mass spectrometer (to be abbreviated as QMS hereinafter) <b>29</b> set on the inner wall surface of a process vessel <b>12</b> as a sensor for detecting the state of a plasma P generated in a process chamber <b>11</b>. The QMS <b>29</b> detects the number of plasma ions reaching a predetermined region of the inner wall surface of the process vessel <b>12</b>.

0104The detection result of the QMS <b>29</b> is output to a controller <b>36</b>A. The controller <b>36</b>A has the same function as that of the controller <b>36</b> shown in <figref idref="DRAWINGS">FIG. 1</figref> except that it controls the reactance of a filter <b>27</b> on the basis of the detection result of the QMS <b>29</b> set on the inner wall surface of the process vessel <b>12</b>.

0105When the first control mode appropriate for an etching process of a wafer W is selected, the controller <b>36</b>A controls the reactance of the filter <b>27</b> in such a direction that the number of ions detected by the QMS <b>29</b>, i.e., the number of ions reaching the inner wall surface of the process vessel <b>12</b>, decreases. Then, the plasma P does not diffuse in the entire process chamber <b>11</b> but is distributed over a region opposing the support surface of a susceptor <b>21</b> at a high density. Thus, in the same manner as with the etching apparatus shown in <figref idref="DRAWINGS">FIG. 1</figref>, the etching process can be performed more efficiently than in the prior art, and the service life of the process vessel <b>512</b> can be prolonged.

0106When the second control mode appropriate for cleaning of the interior of the process chamber <b>11</b> is selected, the controller <b>36</b>A controls the reactance of the filter <b>27</b> in such a direction that the number of ions detected by the QMS <b>29</b>, i.e., the number of ions reaching the inner wall surface of the process chamber <b>11</b>, decreases. Thus, the interior of the process chamber <b>11</b> can be cleaned efficiently.

0107In place of the QMS <b>29</b>, a current sensor for detecting the value of a current flowing from the process vessel <b>12</b> to ground may be used. In this case, the controller may control the reactance of the filter <b>27</b> in such a direction that the current value detected by the current sensor decreases in the first mode, and in such a direction that the current value detected by the current sensor increases in the second mode.

0108In the etching apparatus shown in <figref idref="DRAWINGS">FIG. 1</figref>, the filter <b>27</b> is controlled on the basis of an electrical signal flowing from the susceptor <b>21</b> to ground, and in the etching apparatus shown in <figref idref="DRAWINGS">FIG. 5</figref>, the filter <b>27</b> is controlled on the basis of an electrical signal flowing from the process vessel <b>12</b> to ground. Alternatively, the two control schemes may be combined, and the filter <b>27</b> may be controlled optimally on the basis of the two electrical signals.

Third Embodiment

0109<figref idref="DRAWINGS">FIG. 6</figref> is a view showing the arrangement of an etching apparatus according to the third embodiment of the present invention. In <figref idref="DRAWINGS">FIG. 6</figref>, the same portions as in <figref idref="DRAWINGS">FIG. 1</figref> are denoted by the same reference numerals, and a description thereof will be omitted when appropriate.

0110The etching apparatus shown in <figref idref="DRAWINGS">FIG. 6</figref> is a two-frequency type etching apparatus having, in addition to an RF power supply <b>34</b> which supplies an RF power for exciting a plasma P, an RF power supply <b>24</b> which supplies an RF power for applying a bias across an upper electrode <b>31</b> and susceptor <b>21</b>. When the bias is applied across the upper electrode <b>31</b> and susceptor <b>21</b>, etching can be performed while controlling the energy and anisotropy of the plasma P. The RF power supply <b>24</b> may suffice as far as it outputs an RF power with a frequency of about 100 kHz to 13 MHz and a power value of about 1.0 kW to 5.0 kW. In this embodiment, note that the RF power supply <b>24</b> outputs an RF power with a frequency of 2 MHz and a power value of 1.5 kW. When cleaning is to be performed, an output from the RF power supply <b>24</b> is stopped, or the RF power supply <b>24</b> outputs a low power of 100 W to 500 W.

0111The RF power supply <b>24</b> is connected to the susceptor <b>21</b> through a matching circuit <b>25</b>. The matching circuit <b>25</b> matches the impedances of the RF power supply <b>24</b> and susceptor <b>21</b>, and is formed of, e.g., a variable capacitor. The capacitor of the matching circuit <b>25</b> is controlled by a controller <b>26</b>.

0112A support <b>32</b> having the same potential as that of the upper electrode <b>31</b> is grounded through a second filter <b>37</b> formed of a resonance circuit having a variable reactance. The path extending from the susceptor <b>21</b> to reach ground through the upper electrode <b>31</b>, support <b>32</b>, and filter <b>37</b> will be called the second path. When the reactance of the filter <b>37</b> is changed, the impedance of the second path against the frequency (2 MHz) of the RF power supplied to the susceptor <b>21</b> can be adjusted.

0113Furthermore, a sensor <b>38</b> which detects an electrical signal flowing through the filter <b>37</b> and a control means for controlling the reactance of the filter <b>37</b> on the basis of the detection result output from the sensor <b>38</b> are provided. In the etching apparatus shown in <figref idref="DRAWINGS">FIG. 6</figref>, the controller <b>26</b> for the matching circuit <b>25</b> is provided with the function of the control means for the filter <b>37</b>.

0114Regarding the sensor <b>38</b> and controller <b>26</b>, they have the same arrangements and the same functions as those of the sensor <b>28</b> and controller <b>36</b>, respectively, shown in <figref idref="DRAWINGS">FIG. 1</figref>. Note that the controller <b>26</b> as the control means for the filter <b>37</b> suffices as far as it has the function of controlling the reactance of the filter <b>37</b> in such a direction that the impedance of the second path against the frequency of the RF power supplied to the susceptor <b>21</b> decreases.

0115The filter <b>37</b> will be further described.

0116<figref idref="DRAWINGS">FIG. 7</figref> is a circuit diagram showing the arrangement of the filter <b>37</b>. The filter <b>37</b> has a first module <b>37</b>A for blocking a DC component from passing therethrough, a second module <b>37</b>B with a variable reactance against the frequency of the RF power supplied to the susceptor <b>21</b>, and a third module <b>37</b>C for blocking the frequency (60 MHz) of the RF power supplied to the upper electrode <b>31</b> from passing therethrough.

0117When the RF power supply <b>24</b> supplies an RF power to the susceptor <b>21</b>, a DC voltage of about several hundred V is generated in the upper electrode <b>31</b>. The first module <b>37</b>A is formed of, e.g., a capacitor <b>37</b><i>p</i>, and blocks the DC component from passing from the upper electrode <b>31</b> to ground, thus preventing short-circuiting of the DC component.

0118The second module <b>37</b>B is formed of, e.g., a series circuit (LC series resonance circuit) of a coil <b>37</b><i>r </i>and capacitor <b>37</b><i>q</i>. In this case, it suffices as far as at least one of the inductance of the coil <b>37</b><i>r </i>and the capacitance of the capacitor <b>37</b><i>q </i>is variable. In this embodiment, the inductance of the coil <b>37</b><i>r </i>is variable, while the capacitance of the capacitor <b>37</b><i>q </i>is fixed. When the second module <b>37</b>B is an LC series resonance circuit as shown in <figref idref="DRAWINGS">FIG. 7</figref>, the capacitor <b>37</b><i>q </i>of the second module <b>37</b>B may also serve as the capacitor <b>37</b><i>p </i>of the first module <b>37</b>A.

0119The third module <b>37</b>C is formed of, e.g., a parallel circuit of a coil <b>37</b><i>t </i>and capacitor <b>37</b><i>s</i>, and is designed to have a high impedance against a frequency in the vicinity of the frequency (60 MHz) of the RF power to be supplied to the upper electrode <b>31</b>. Thus, the RF power supplied to the upper electrode <b>31</b> can be prevented from flowing to the filter <b>37</b>.

0120A blocking plate <b>37</b>D made of aluminum or ion, which performs electrostatic blocking or electromagnetic blocking, is arranged between the first and second modules <b>37</b>A and <b>37</b>B and the third module <b>37</b>C. When electrical interference occurs between the third module <b>37</b>C and the first and second modules <b>37</b>A and <b>37</b>B, the band-blocking ability of the third module <b>37</b>C decreases largely, and power loss due to the filter <b>37</b> occurs. Then, not only the power efficiency decreases, but depending on the case, an excessive current may also flow through the filter <b>37</b> to burn it. When the blocking plate <b>37</b>D is provided, these problems can be prevented.

0121The reactance of the filter <b>37</b> having the above arrangement is designed such that under predetermined process conditions, a resonance frequency f2 of the second path becomes equal to the frequency (2 MHz) of the RF power supplied to the susceptor <b>21</b> and the impedance against this frequency becomes minimum. The range of the reactance is set such that even when an inductance L_SHand capacitance C_SHobtained by an ion sheath SH change in accordance with the process conditions, the impedance of the second path can be minimized. This is the same as in the filter <b>27</b> shown in <figref idref="DRAWINGS">FIG. 1</figref>.

0122For example, to obtain f2=2 MHz under the following process conditions, C=1,500 pF and 1 μH≦L≦50 μH are given. <ul id="ul0007" list-style="none"><li id="ul0007-0001" num="0000"><ul id="ul0008" list-style="none"><li id="ul0008-0001" num="0123">RF power supplied to the upper electrode <b>31</b><ul id="ul0009" list-style="none"><li id="ul0009-0001" num="0124">frequency: 60 MHz, power value: 1.0 kW to 5.0 kW</li></ul></li><li id="ul0008-0002" num="0125">RF power supplied to the susceptor <b>21</b><ul id="ul0010" list-style="none"><li id="ul0010-0001" num="0126">frequency: 2 MHz, power value: 1.0 kW to 5.0 kW</li></ul></li><li id="ul0008-0003" num="0127">process pressure: 0.6 Pa to 10 Pa</li><li id="ul0008-0004" num="0128">process gases: Ar=200 sccm to 400 sccm, <ul id="ul0011" list-style="none"><li id="ul0011-0001" num="0129">O₂=5 scam to 20 scam</li></ul></li></ul></li></ul>

0130Alternatively, the filter <b>37</b> may be formed by using a fixed inductance L (e.g., 5 μH or more) sufficiently larger than the upper limit of the variable range of the inductance L_SHobtained by the ion sheath SH, or a fixed capacitance C (e.g., 200 pF or less) sufficiently smaller than the lower limit of the variable range of the capacitance C_SHobtained by the ion sheath SH.

0131In a filter <b>127</b>, a third module (not shown) for blocking a frequency of 2 MHz is series-connected to the first and second modules <b>27</b>A and <b>27</b>B shown in <figref idref="DRAWINGS">FIG. 2</figref>, so the 2-MHz RF power supplied from the RF power supply <b>24</b> to the susceptor <b>21</b> does not flow to the filter <b>127</b> which is also connected to the susceptor <b>21</b>. In this case, the reactance of the filter <b>127</b> is designed such that a resonance frequency f1 of the entire first path including the third module becomes equal to the frequency (60 MHz) of the RF power supplied to the upper electrode <b>31</b>. When a blocking plate of aluminum or iron which performs electrostatic blocking or electromagnetic blocking is arranged between the first and second modules <b>27</b>A and <b>27</b>B and the third module, a decrease in power efficiency and burning can be prevented.

0132Alternatively, a matching circuit <b>125</b> including a filter <b>127</b> may be used, as shown in <figref idref="DRAWINGS">FIG. 8</figref>.

0133The etching apparatus has the arrangement described above, and control operation is performed on the basis of a current flowing through the filter <b>37</b> in such a direction that the impedance of the entire second path against 2 MHz decreases. Then, of the RF power supplied to the susceptor <b>21</b>, its proportion directed to the process vessel <b>12</b> decreases, while its proportion directed to the upper electrode <b>31</b> increases. Hence, the energy and anisotropy of the plasma P occurring upon application of a bias can be controlled more accurately than in the prior art. Even when the process conditions change and accordingly the state of the ion sheath SH changes, the energy and anisotropy of the plasma P can be controlled with the same accuracy.

0134The bias applied across the upper electrode <b>31</b> and susceptor <b>21</b> may be either a DC bias or pulsed bias. Hence, a DC power supply may be used in place of the RF power supply <b>24</b>. As the sensor for detecting the state of the plasma P, a sensor set to the inner wall surface of the process vessel <b>12</b>, like the QMS shown in <figref idref="DRAWINGS">FIG. 5</figref>, may be used.

Fourth Embodiment

0135The controller <b>36</b> shown in <figref idref="DRAWINGS">FIG. 1</figref> may have a plurality of control modes that realize different plasma distributions in the process chamber <b>11</b>, and a switch (not shown) for performing switching operation among these control modes.

0136For example, in a process that produces a large amount of deposits to attach to the inner wall surface of the process vessel <b>12</b>, a control mode with which the amount of plasma P reaching the inner wall surface of the process vessel <b>12</b> increases is selected, and the reactance of the filter <b>27</b> is controlled. Then, deposits do not easily attach to the inner wall surface.

0137In a process that produces a small amount of deposits to attach to the inner wall surface of the process vessel <b>12</b>, a control mode with which the amount of plasma P reaching the inner wall surface of the process vessel <b>12</b> becomes smaller than that described above is selected, and the reactance of the filter <b>27</b> is controlled. In this case, the amount of plasma P reaching the inner wall surface may be comparatively increased to such a degree that no deposit attaches to the inner wall surface at all, or may be comparatively decreased to such a degree that deposits stably attach to the inner wall surface.

0138Therefore, when the process conditions are changed, the control mode is switched in accordance with the characteristics of the process, and the amount of deposits to attach to the inner wall surface of the process vessel <b>12</b> is adjusted, so particles formed from peeled-off deposits can be decreased. Then, the yield of elements to be formed on the wafer W can be increased.

0139The controller <b>36</b> shown in <figref idref="DRAWINGS">FIG. 1</figref> may have the function of changing the reactance of the filter <b>27</b> during the etching process.

0140For example, control operation may be performed by periodically changing the amount of plasma P to reach the inner wall surface of the process vessel <b>12</b> during the process, so the deposits attaching to the inner wall surface of the process vessel <b>12</b> stabilize.

0141The deposits that are to attach to the inner wall surface of the process vessel <b>12</b> do not attach easily if the temperature of the inner wall surface increases. In view of this, the temperature of the inner wall surface of the process vessel <b>12</b> may be measured, and the amount of plasma P to reach the inner wall surface may be changed during the process on the basis of the measured temperature, so that the deposits attach stably. Alternatively, the lapse time since the start of generation of the plasma P may be measured, and the same control operation may be performed on the basis of the measured time.

0142When the deposits attaching to the inner wall surface of the process vessel <b>12</b> are stabilized in the above manner, the deposits can be prevented from peeling off to form particles. This can improve the yield of the elements to be formed on the wafer W.

0143When the reactance of the filter <b>27</b> is changed during the etching process, the amount or nature of radicals to attach to the inner wall surface of the process vessel <b>12</b> can be changed. If the amount or nature of the radicals to attach to the inner wall surface changes, components or amount dissociating from the inner wall surface changes. If optimal radicals are selected, the process performance can be improved.

0144At the etching end point, the constitution of the radicals in the process chamber <b>11</b> changes, and the attaching easiness of the radicals to the inner wall surface or dissociating easiness of the radicals from the inner wall surface changes. Hence, as one of the process conditions, the reactance of the filter <b>27</b> may be changed, so the constitution of the radicals does not change at the etching end point.

0145The reactance of the filter <b>27</b> may be controlled by the controller <b>36</b> in accordance with a preset procedure, or on the basis of a detection signal such as an EPD (End Point Detection) signal indicating the etching end point.

0146The above function of the controller <b>36</b> may be provided to the controller <b>26</b> shown in <figref idref="DRAWINGS">FIG. 6</figref> as a function for the filter <b>37</b>.

Fifth Embodiment

0147The controller <b>36</b> shown in <figref idref="DRAWINGS">FIG. 1</figref> may have the function of appropriately controlling the reactance of the filter <b>27</b> so that occurrence of abnormal discharge in the process chamber <b>11</b> is suppressed.

0148For example, the larger the value of the current flowing through the filter <b>27</b>, the more unlikely abnormal discharge occurs. When the value of the current flowing through the filter <b>27</b> is detected by the current sensor <b>28</b>A and the reactance of the filter <b>27</b> is controlled by the controller <b>36</b> in such a direction that the detected current value increases, thus maximizing the current value, then occurrence of abnormal discharge can be suppressed.

0149The reactance of the filter <b>27</b> may be controlled on the basis of the value of the voltage applied to the filter <b>27</b>, in place of the value of the current flowing through the filter <b>27</b>.

0150Whether the maximum value of the current flowing to the filter <b>27</b> and the like are adjusted to adjustment values that are effective for suppressing abnormal discharge can be checked from the detection result of the sensor <b>28</b>.

0151This function of the controller <b>36</b> may be provided to the controller <b>26</b> shown in <figref idref="DRAWINGS">FIG. 6</figref> as a function for the filter <b>37</b>.

0152As has been described above, according to the above embodiments, a sensor for detecting the state of the plasma, and a control means for controlling the circuit characteristics of the first filter connected between the susceptor and ground in accordance with the detection result are provided. Thus, the impedance of the first path, which extends from an electric field generating means for generating an AC field at a position opposing the support surface of the susceptor to reach ground through the susceptor and filter, can be adjusted in accordance with the state of the plasma. A preferable plasma distribution in accordance with the object of the plasma process can be realized, so the process efficiency can be improved. Etching of the inner wall surface of the process chamber with the plasma can be suppressed, so the service life of the process chamber is prolonged, and occurrence of particles can be decreased.

0153While the above description exemplifies a parallel-plate etching apparatus, the present invention can also be applied to an induction-coupled plasma etching apparatus, microwave plasma etching apparatus, and the like. Naturally, the present invention can be applied not only to an etching apparatus but also to other plasma processing apparatuses such as a plasma CVD apparatus.